The present study deals with calculating optimal exchanged grinding wheel diameter to get the minimum manufacturing time when external grinding tool steel. To do that, four input factors covering the initial grinding wheel diameter D0, the radial grinding wheel wear per dress Wpd, the wheel life Tw, and the total dressing depth aed. Also, for weighing the effect of the process parameters on the optimal exchanged wheel diameter dop, a simulation experiment was designed and performed. In addition, a proposed equation to find the optimal exchanged wheel diameter was given